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                    <h1 class="description center-align post-title">PHP性能如何优化</h1>
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                <h2 id="变量"><a href="#变量" class="headerlink" title="变量"></a>变量</h2><blockquote>
<p>变量的性能排行：局部变量     &gt;    全局变量    &gt;    类属性    &gt;    未定义的变量</p>
</blockquote>
<ol>
<li>变量大小，注意变量大小是节约内存的最有效的手段。对于来自表单、数据库和文件缓存的数据都需要控制变量的大小。因为<code>CPU</code>要处理的数据是来源于内存。</li>
<li>变量的有效期，使用<code>unset()</code>函数注销不需要的变量是一种好习惯，将一些不需要的变量立即注销可提高内存的使用率。</li>
<li>变量类型，初始化变量请注意其变量类型，一个变量在执行过程中，最好只有一种类型状态。</li>
<li>临时变量，是处理业务逻辑的临时存储，这些都是需要消耗内存的。如果临时变量使用结束请立即注销。</li>
<li>静态变量，对于一些需要由复杂业务产生的变量，如果在程序的执行过程中多次产生并使用，可以考虑使用静态变量，减少程序的<code>CPU</code>执行次数。</li>
</ol>
<h2 id="循环"><a href="#循环" class="headerlink" title="循环"></a>循环</h2><ol>
<li>尽量减少循环的次数</li>
<li>尽量减少循环嵌套的层次</li>
<li>避免在循环内有过多的业务逻辑</li>
<li>不要循环包含文件</li>
<li>不要循环执行数据库操作</li>
<li>优先使用<code>foreach</code>，它比<code>for、while</code>效率更高</li>
<li>不要把<code>count、strlen、sizeof</code>放入<code>for</code>循环条件语句中</li>
<li>保持循环体内的业务逻辑清晰</li>
</ol>
<h2 id="函数"><a href="#函数" class="headerlink" title="函数"></a>函数</h2><ol>
<li><p>函数职责清晰，一个函数只干一件事，不杂糅过多的业务逻辑</p>
</li>
<li><p>函数代码体不超过20行，反之考虑拆分</p>
</li>
<li><p>优先使用<code>PHP</code>内置函数</p>
</li>
<li><p>常量与函数同时能干一件事，优先使用常量</p>
<p>例如：</p>
<pre class=" language-php"><code class="language-php"><span class="token function">phpversion</span><span class="token punctuation">(</span><span class="token punctuation">)</span>    <span class="token operator">&lt;</span>    <span class="token constant">PHP_VERSION</span>
<span class="token function">get_class</span><span class="token punctuation">(</span><span class="token punctuation">)</span>        <span class="token operator">&lt;</span>    <span class="token constant">__CLASS__</span>
<span class="token function">is_null</span><span class="token punctuation">(</span><span class="token punctuation">)</span>        <span class="token operator">&lt;</span>    <span class="token keyword">NULL</span>
<span class="token comment" spellcheck="true">// 等等。。。</span></code></pre>
</li>
<li><p><code>echo</code>的性能好于<code>print</code>，输入多个变量的使用<code>echo $str1,$str2,$str3</code>，不用<code>.</code>连接符</p>
</li>
<li><p>使用<code>$_SERVER[&#39;REQUEST_TIME&#39;]</code>替换<code>time()</code></p>
</li>
<li><p>字符串替换</p>
<pre class=" language-php"><code class="language-php"><span class="token function">strtr</span><span class="token punctuation">(</span><span class="token punctuation">)</span>    <span class="token operator">></span>    <span class="token function">str_replace</span><span class="token punctuation">(</span><span class="token punctuation">)</span>    <span class="token operator">></span>    <span class="token function">preg_replace</span><span class="token punctuation">(</span><span class="token punctuation">)</span>    <span class="token operator">></span>    <span class="token function">epreg</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code></pre>
</li>
<li><p>发挥<code>trim</code>最大功效，替换<code>substr</code></p>
<pre class=" language-php"><code class="language-php"><span class="token variable">$file_path</span> <span class="token operator">=</span> <span class="token function">trime</span><span class="token punctuation">(</span><span class="token variable">$filename</span><span class="token punctuation">,</span> <span class="token string">'/'</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token string">'/'</span><span class="token punctuation">;</span></code></pre>
</li>
<li><p><code>isset/empty</code>虽然两个函数功能有所差异，但在同样情况下推荐使用<code>empty()</code></p>
</li>
<li><p><code>isfile/file_exists</code>两个函数的功能有所不同，<code>file_exists</code>既可判断文件是否存在，也可以判断目录是否存在，在同样的情况下推荐使用<code>is_file</code></p>
</li>
</ol>
<h2 id="文件"><a href="#文件" class="headerlink" title="文件"></a>文件</h2><ol>
<li>减少文件包含数，减少磁盘<code>IO</code></li>
<li>使用完整路径，或者容易转换的相对路径。避免在<code>include_path</code>查找</li>
<li>文件的代码行数不要超过2000行</li>
<li><code>require_once/include_once</code>效率低于<code>require/include</code>，需要额外的去查看系统是否已经调用过这个文件，因为它们在一个<code>opcode</code>缓存下的调用非常慢。</li>
<li>程序执行文件用<code>require/require_once</code>，缓存文件用<code>include/include_once</code>。<code>include</code>效率好于<code>require</code>。</li>
<li>优化<code>spl</code>中的文件自动加载机制，参考<code>YII</code></li>
<li>类库文件加载，是否考虑类是否已实例化，可考虑采用设计模式之单例模式</li>
<li>文件读写的并发性</li>
</ol>
<h2 id="面向对象"><a href="#面向对象" class="headerlink" title="面向对象"></a>面向对象</h2><ol>
<li>控制实例的创建的数量</li>
<li>优先使用常量、类常量</li>
<li>优先使用静态变量，静态属性</li>
<li>类的结构合理</li>
<li>面向接口编程</li>
<li>封装变化点</li>
<li>依赖于抽象，不依赖于细节</li>
<li>优先使用静态成员</li>
<li>类的接口清晰稳定，类的职责单一，类与类的通信合理</li>
<li>使用常量的好处：编译时解析，没有额外的开销，杂凑表更小，所以内部查找更快，类常量仅存在于特定的【命名空间】，所以杂凑名更短，代码更干净，使除错更方便</li>
</ol>
<h2 id="字符串"><a href="#字符串" class="headerlink" title="字符串"></a>字符串</h2><blockquote>
<p>用单引号替代双引号引用字符串；避免检索字符串中的变量</p>
</blockquote>
<h2 id="运算"><a href="#运算" class="headerlink" title="运算"></a>运算</h2><ol>
<li>用<code>i += 1</code>代替<code>i = i + 1</code>，符合<code>C/C++</code>的习惯，效率还高</li>
</ol>
<h2 id="数组"><a href="#数组" class="headerlink" title="数组"></a>数组</h2><blockquote>
<p>多维数组尽量不要循环嵌套赋值</p>
</blockquote>
<h2 id="判断"><a href="#判断" class="headerlink" title="判断"></a>判断</h2><ol>
<li><p>逻辑判断优先使用<code>switch</code>，对于业务逻辑相对较多情况请选择<code>if/else</code>，提高代码的可读性</p>
</li>
<li><p>尽量控制<code>if/else</code>判断的个数，如果太多请考虑功能优化或代码优化，或使用三元运算符</p>
</li>
<li><p>尽量使用恒等于用于比较判断，恒等的效率高于等于，而且还能避免一些类型强制转换的错误</p>
</li>
<li><p><code>if/else</code>与<code>&amp;&amp;</code>单条语句判断请选择<code>&amp;&amp;</code>的形式，它的效率高于<code>if/else</code>，如下：</p>
<pre class=" language-php"><code class="language-php"><span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token variable">$a</span> <span class="token operator">==</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token variable">$b</span> <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment" spellcheck="true">// 优化</span>
<span class="token punctuation">(</span><span class="token variable">$a</span> <span class="token operator">==</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token operator">&amp;&amp;</span> <span class="token variable">$b</span> <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span></code></pre>
</li>
</ol>
<h2 id="缓存"><a href="#缓存" class="headerlink" title="缓存"></a>缓存</h2><ol>
<li>使用<code>PHP</code>缓存，缓冲<code>opcode</code></li>
<li>使用<code>memcache/nosql</code></li>
<li>使用内存数据库</li>
<li>使用文件缓存</li>
<li>缓冲功能</li>
</ol>
<h2 id="其他"><a href="#其他" class="headerlink" title="其他"></a>其他</h2><ol>
<li>少用<code>@</code>符号，严重影响性能</li>
<li>适时关闭远程资源连接如数据库，<code>ftp</code>，<code>socket</code>等，适时清理这些资源</li>
</ol>
<h2 id="性能检测工具"><a href="#性能检测工具" class="headerlink" title="性能检测工具"></a>性能检测工具</h2><ol>
<li><code>Web Server</code></li>
<li><code>ab</code></li>
<li><code>http_load</code></li>
<li><code>xdebug</code></li>
</ol>

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使用数组进行模拟栈的实现

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StackMoc.java
/**
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                            给憨憨写的阶乘的实现原理
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==前2
                        
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